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mist, and between 10 and 1 1 o'clock cleared up, leaving only a haziness in the
air behind it : the weather quite calm, wind about n. w.

These parhelia are commonly seen with a circle or halo round the sun, con-
centrical to it, and passing through the disks of the spurious or mock-suns.
But there was not the least appearance of such a circle here, it having only a
tendency towards one, when it was seen with the rainbow colours.

The other phenomenon, was that pretty common one of the aurora borealis,
of an uncommon appearance. A little after 3 o'clock, the northern hemi-
sphere was obscured by a dusky red vapour, in which, by degrees, appeared
several very small black clouds near the horizon. The first eruption of the
lights was within a quarter of an hour, full east, from behind one of the small
dark clouds, and soon after several others full north. These streams of light
were of the same dusky red colour as the vapour, just appeared, and vanished
instantly. He saw 8 or 10 of these at once, about the breadth of the rainbow,
of different heights, several degrees above the horizon, which looked like so
many red pillars in the air ; and no sooner did they disappear, but others showed
themselves in different places. In about half an hour, this colour of the va-
pour gradually changed towards the usual white, and spread much wider and
higher ; and after that, appeared as common.


Observations of two Parhelia, or Mock-Suns, seen at Witlemherg, in Saxony,
on Dec.3\, 1735. 0.5. By John Frid. fVeidler, F. R. S. i^c. N° 445,
p. 54.

Dec. 31, 1735, o. s. a little after 10 in the morning, being informed that
several suns were seen in the heavens, Mr. W. went into his garden, and
immediately saw near the sun s, on its left or western side, the parhelion b,
as large as the true sun, fig. 15, pi. 5. This mock-sun was amidst small,
round, white clouds, set thick, and close to one another. The middle of this
mock-sun shone with so great a light, that the naked eye could not bear it ;
so that he viewed it attentively through a glass darkened with the smoke of
a wax-candle. The light of the parhelion b appeared much weaker than that
of the true sun. Its circumference, facing the sun, was red : but that part of
the stream fg, which was towards the sun, was purple. Within the red
border appeared the other colours of the rainbow, as yellow, green and azure ;
the stream bh was likewise embellished with red and yellow. Both edges of
this were reddish, and its middle yellowish. The sun s was 15°-f above
the horizon ; and its image b was near the same altitude : the distance from s
to B was '20°: the arch fg was near 6° in length. Most of the south-
ern part of the hen)ibphere was overspread with white clouds, interspersed
with some darker ones. There were some thin clouds before the true sun,
through which its rays easily passed. When thicker clouds surrounded the
sun, the brightness of the parhelion was lessened : the parhelion was now and
then hidden by dark clouds. Soon after first observing the parhelion b, was
seen the beautiful rainbow ode, parallel to the horizon, with its horns turned
to the north. It had the usual colours of the rainbow, all very distinct. The
purple was on the side facing the sun ; next to it was the yellow, then the
green, and last the azure. The point d was Q\° distant from the horizon;
therefore the diameter of the rainbow was 58° : however, only a part of the
rainbow ode was seen, the ends of which were sometimes but 38° from one
another: for more or less of it appeared at different times, but scarcely above
a 4th part of its circumference at any time. It lasted till the sun and most
part of the sky was overcast by thick clouds. The thickness of the rainbow
CK, as well as I could estimate by the bare eye, was 1° of a great circle.

From another place, whence he had a full view of tl)e hemisphere, a little
before 11 , he saw another parhelion a to the east, 20° from the sun, as the
former was, and raised 15° above the horizon. This mock-sun was not infe-
rior to the other b, in brightness, for the naked eye could no more bear it


than that: its light was white; its figure round, audits size equal to that of
the sun s. This parhelion a shot out the stream il, which was rectlinear,
white and resplendent, 8° long, and void of colours ; and it lasted somewhat
longer than the former, without changing its figure. On the sun's being hid
by thick clouds, about 4- hour after eleven, both these mock-suns disappeared ;
but they became visible again, on the sun's shining bright.

The whole of the phaenomena observed in these parhelia comes to this :
that the true sun, s, was accompanied by two parhelia, both 20° distant from
the sun, one on each side, and having nearly the same altitude with the sun
from the horizon. Above the parhelia, part of a rainbow surrounded the
zenith; and each of the parhelia sent forth a bright luminous strean) or tail,
one rectilinear and white, the other soraewliat curved and coloured. More-
over, from the western parhelion, a stream parallel to the horizon, and some-
what pointed, extended itself on the side opposite to the sun ; and this scene
lasted the 2 hours of 10 and 1 1 before noon, till thick clouds put an end to it.
There was no appearance of an entire crown, such as usually accompanies
parhelia, and encircles the sun.

An Observation of three Mock-Suns seen in London, Sept. 17, 1736. By
Martin Folkes, Esq. F. Pr. R. S. N" 445, p. 59.

Sept, 17, 1736, as Mr. Folkes was reading a little after 7 in the morning,
in a room looking towards the north-east, he accidentally noticed an odd stream
of coloured light, shooting upwards from the sun, shining through a thin
waterish cloud ; but recollecting the appearance was several degrees more nor-
therly than the sun's true place at that time, he went to the window, and found
what he had taken for the sun was a parhelion, shooting out a short horizontal
stream or tail towards the north ; the sun itself shining pretty bright and clear
at the same time. He also observed, that the stream he had at first seen, was
part of an arch concentric to the sun, and passing through the parhelion : this
arch was for a good way tolerably defined, and tinged with red on the inside,
and a bluish white on the other. Casting his eye to the other side the sun,
he perceived a second parhelion, at the same distance from him, towards the
south, though not yet so bright as the first. He then went up to the leads of
his house, where he soon found the phenomenon considerably to improve, the
arch round the sun forming itself into more than a semicircle, reaching almost
to the horizon northward, and with very little discontinuance beyond the second
parhelion towards the south. He then began to perceive a third parhelion,
where the circle surrounding the sun would have been cut by the vertical

VOL. vni. T


passing through him ; and in the same place his circle was touched by the arch
of another, in some sort confounding itself with it in the place where the third
parhelion appeared : this was a good deal fainter than the other two, and the
last arch extended but a little way, so as to be difficult to determine where its
centre lay ; this arch was coloured also, but with red on its convex part. He
had some time before this begun to see also another circle, surrounding the
sun at the distance of about 45°, which appeared to be about twice the distance
of the first ; and this also increasing while he was considering it, became little
less than a semicircle, being also tinged with red like the other on the inner
side. When the circle had thus pretty well formed itself, he also discovered
the arch of a 4th, touching this, or rather confounding itself with it, in its
highest part, and surrounding, as it seemed, the zenith. Of this last circle
he saw, when it was most complete, better than half, and it was much stronger
coloured than any of the others, being of a bright red on its convex part, and
a good blue on the concave. In the part where this circle confounded itself
with the larger of those that were concentric to the sun, their common part
was nearly white, and brighter than the rest, though hardly enough to call it
a 4th parhelion. The principal mock-suns continued tolerably bright till near
8 o'clock, the southern part of the phenomenon improving as the northern
decayed ; and the southern parhelion was once so bright, that, taking the ad-
vantage of a place where a chimney shaded the true sun, it cast a very visible
shadow : the white and luminous horizontal tail also, that went from this par-
helion, was much longer than that of the other, reaching at one time beyond
the outer of the two concentric circles. The parhelia themselves, though very
luminous, were, however, never defined with any exactness as to their discs,
but looked as we sometimes see the sun through a thin whitish cloud, and they
were themselves of a reddish colour on that side next the true sun. About 8
the phenomenon was sensibly decreased, and had entirely disappeared by 20"
after. All these appearances are exhibited in fig. l6, pi. 5.

Of a Rupture of the Ileum from an external Contusion, in a Letter from
Christian Wolf, Professor of Mathematics at Marpurg, &c. to Wm. Rutty,
M. D. formerly Secretary to the R. S. Dated March 3, 1731. An Abstract
from the Latin. N° 445, p. 6l.

Professor Wolf here states that a labourer had received a fatal accident from
a large stone falling upon the abdomen, in such manner as to occasion a con-
tusion, but no laceration. The man died very unexpectedly the day after the
accident. On opening the body, a large rent was discovered in the ileum, and
its contents were found effused into the cavity of the abdomen.


Some new Statical Experiments. By J. T. Desaguliers, LL. D. F. R. S,

N° 445, p. 62.

When a long and heavy body, lying on the ground, is to be raised up at
one end, like a lever of the second kind, while the other end keeps its place,
and becomes the centre of its motion; the prop used to support it at any point
in its whole length, sustains a certain pressure from the beam. Now these ex-
periments are to show, by a force drawing always in the direction of the prop,
what is the quantity of the pressure on the prop, according to its length, and
to the angle which it makes with the beam, or with the horizon, and to the
distance from the centre of motion of the beam at which the prop is applied.
For when the prop is taken away, the force drawing in the direction of the
prop will keep the beam in equilibrio ; and a force ever so little superior to the
friction added to the power, will make it overpoise the beam, and raise it
higher ; but overcome the power and bring down the beam, if it be added or
applied to the beam.

Though in every case and experiment we have this analogy, taken from me-
chanical principles, viz. that, — The intensity of the power : Is to that of the
weight : : As the distance of the line of direction of the weight : Is to the
distance of the line of direction of the power; — ^yet to find those distances
nicely in the several applications of the prop, we must have recourse to geo-
metrical constructions and reasonings. With these and the algebraical ex-
pressions of the same, the experiments exactly agree.

In the machine here used, the iron bar, or parallelipiped representing the
heavy body, weighs 12 drams, 12 dwt. 12 grains, or 6060 grains; and its
centre of gravity is at the distance of 2O-I- inches from its centre of motion.
The props used are, the one of 5, and the other of 10 inches. To over-
come the friction, allowed for by certain rules in all cases, the Dr. used a nice
brass pulley, of 3 inches diameter, its pivots only -j-J-^ of an inch in diameter ;
so that the 6oth part of the power added to it, will in all cases overcome the

Case I. In which the Prop is perpendicular to the Horizon, exemplified by

two Experiments.

Exper. 1. — The prop is 5 inches, and placed under a point in the bar, 10
inches from the centre of motion. Here the power acting in the direction of
the prop, able to keep the bar in that situation, or the pressure sustained by
the prop, will be found 250 oz. 1 7 dwt. 1 5 grains ; and the friction 8 dwt.
15 grains. The foot of the prop is to be at 8 inches and -^ from the centre
of motion.

T 2


Exper. 2. — If the same prop, of 5 inches, be placed under a point in the
bar at 30 inches from the centre of motion, the power or pressure will be 8 oz.
12 dwt. 13 gr. and the friction equal to 2 dwt. 21 gr. The foot of the prop is
to be distant from the centre of motion 1Q inches -/oV-

Case II. In which the Prop is perpendicular to the Bar, exemplified by three


Exper. ] . — Now let the prop, still 5 inches long, be placed so as to be per-
pendicular to the bar at a point 12 inches from the centre of motion. Here
the power expressive of the pressure should be 1 9 oz. 18 dwt. 4 gr. and the
friction 6 dwt. 15gr.; but on account of a correction necessary to be made to
this, because the bar is thick as well as heavy, and the centre of gravity above
the surface to which the prop is applied, the power or pressure sustained will be
only IQ oz. 15 dwt. 5 gr. and the friction 6 dwt. 14gr. The distance of the
foot of the prop in this case is 13 inches from the centre.

Exper. 1. — ^The prop here is JO inches long, still perpendicular to the bar,
under a point in the bar, 24 inches from the centre. The power equal to the
pressure sustained, should be, if the bar was only heavy, and not thick, g oz.
J 9 dwt. 4 gr.; the friction 3 dwt. 1 l^gr.; but with the proper correction, ex-
plained hereafter, it must be only 9 oz. 17 dwt. 15 gr.; the friction 7 dwt. 7 gr.
Here the foot of the prop is to be 26 inches from the centre.

Exper. 3. — If the end of the prop be placed under a point in the bar, so
that the horizontal distance of the foot of the prop be exactly equal to the dis-
tance of the centre of gravity from the said centre of motion, viz. 20.5 inches,
the power or pressure sustained by the prop will be precisely equal to the weight
of the bar, viz. 12 oz. 12 dwt. 12 gr. In this case, the prop is distant from
the centre of motion on the bar 1 7.9 inches, and the friction 4 dwt. 5 gr.
Case III. In which the angle made by the prop with the horizontal line is given,

either acute or obtuse.

As this case is very intricate, on account of the several powers of the sine
and cosine of the given angle, which are multiplied into the prop, and into the
weight of the beam, we will exemplify it only in one experiment; which is,
when the angle made by the prop, with the horizontal line contained between
the foot of the prop and the centre, is acute: then there is a maximum of pres-
sure, which it appears by experiment is the very same as the calculation gives.
Suppose the angle made by the prop and the horizontal line to be 60 degrees;
the calculation of this maximum shows, that if the prop be 10 inches long,
the distance measured on the bar, to which the upper end of the prop must be
applied, will be 10 inches -^\, the bar itself making then an angle of about
52° 12'; and the horizontal distance between the centre of motion and the foot
of the prop, is then 1 1 inches ■^^.


N. B. Three things are to be remarked in this case:

First, That when the angle made by the prop and the horizontal line, con-
tained between the centre of motion and the foot of the prop, is acute, as in
the last experiment, there is always a maximum: whereas when the same angle
is obtuse, there is no positive maximum; for then the pressure continually in-
creases, the nearer the prop is to the centre of motion.

Secondly, That when the angle of the prop with the horizon is acute, as in
the last experiment, the bar, or long and heavy body, can be raised by applying
the power or prop always with the same angle to the horizon, quite up to a
vertical situation.

Thirdly, That the first case, which is when the prop is perpendicular to the
horizon, is only a particular case of this more general one.
Case IV, Is when the angle made by the prop with that part of the Learn con-
tained bettveen the point to which it is applied, and the centre of motion, is

given, either acute or obtuse.

As the expression of the power in this case, is fully as intricate as in the last,
the Doctor gives only one example or experiment; and, for the greater satisfac-
tion of those that see it, he chose that in which the pressure is in its maximum.
He supposes, as before, the angle made by the prop, still 10 inches long, with
that part of the beam contained between the point to which it is applied, and
the centre of motion, to be acute, and of 6o°; then the maximum of pressure
will be, when the part of the beam intercepted between the centre of motion
and the upper end of the prop is 12 inches -rVo-; the bar is then elevated about
50° 1 3', and the horizontal distance between the centre of motion and the foot
of the prop, is then 1 1 inches -[Vo-

N. B. Observe also in this case, as in the last.

First, If the angle made by the prop, and the part of the beam intercepted
between the point of application and the centre of motion, is acute, there will
always be a maximum. The contrary will happen, if that angle is obtuse.

Secondly, If the angle i* acute, the bar cannot be raised up to a vertical
situation by applying the power or prop constantly with the same acute angle;
but it may be raised quite up, if the angle of ihe prop with the beam is obtuse.

Thirdly, The second case is but a particular case of this general one.

The Apparent Times of the Immersions and Emersions of Jupiter''s Satellites,
for the Year 1739, computed to the Meridian of the Royal Observatory at
Greenwich. By James Hodgson, F. R. S. N" 445, p. 69.

These calculations are omitted for the same reasons as before.


An Account of the Peruvian or Jesuit's Bark.* By Mr. John Gray, F. R. S. at
Carihagena, from some Papers given him by Mr. William Arret, a Scotch
Surgeon, who had gathered it at the Place where it grows in Peru.
N°446, p. 81.

The tree from which the Jesuit's bark is cut, grows in the kingdom of Peru,
in the Spanish West Indies, and is found most commonly in the provinces of
Loxa, Ayavaca, and Quenca, situated between 2 and 5 degrees of south lati-
tude. This tree is tall, and has a trunk rather thicker than a man's thigh, taper-
ing from the root upwards; it has no boughs or branches, till near its top;
where they grow as regular as if lopped artificially, and with the leaves form
exactly the figure of a hemisphere : its bark is of a blackish colour on the out-
side, and sometimes mixed with white spots; whence commonly grows a kind
of moss, called by the Spaniards, barbas; its leaves resemble much the leaves
of our plum-tree, are of a darkish green colour on their upper or concave side,
and on their lower or convex side, reddish ; its wood is as hard as common
English ash, and rather tough than brittle.

There are 4 sorts of the bark of this tree, to which the Spaniards give the
following names, viz. cascarilla colorada, or reddish bark ; amarylla, yellowish ;
crespilla, curling; and blanca, whitish; but Mr. Arrot could only find 2 dif-
ferent sorts of the tree, and he believes that the other 2 sorts of the bark are
owing to the different climates where it grows, and not to a different species
of the tree. The bark called colorada and amarylla, is the best, and it differs
from the blanca in this, that the trunk of the former is not near so thick as that
of the latter; the leaves as described above; whereas those of the blanca are
larger, and of a lighter green colour, and its bark has a very thick spongy sub-
stance, whitish on the outside, and is so tough, that it requires the force of an
axe to slice it from the tree. It is as bitter when cut down as the best sort,
and has then the same effect in intermitting fevers; but when dry and long kept
it turns quite insipid, and is good for nothing. Both sorts have a much surer
and quicker effect in cures when green than when dry. As the bad sort is in
great plenty, and the best very scarce, and hard to be come at, large quantities
of it are cut yearly, and sent with a little of the fine bark to Panama for

The tree of the crespilla is the same with that of the amarylla and colorada,
but it grows in a cold frosty climate { by which means the bark is not only altered
in its quality, but is also whitish on the outside, though cinnamon-coloured

* Cinchona otHcinalis. Linn.


within, and ought in medicines to be rejected. This sort and the blanca grow
plentifully in the province of Ayavaca, 50 leagues from Piura, and 62 from
Payta, a port in the South Sea; as also in Cariamango, Gonsonama, and Xim-
buro, whence they commonly send it to Payta, and there sell it as the best.
The blanca likewise grows in the province of Quenca, and in the mountains of
Caxamarea: but the true and genuine fine Jesuit's bark, which is of a reddish
or yellowish colour, is only found from 5 to about 14 leagues round the city of
Loxa, in the province of Loxa, called generally by the Spaniards, Provincia de
las Calvas. This city is situated between 2 rivers, that run into the great river
Marannon, or of the Amazons, and lies about lOO leagues from Payta, and in
a direct line about 1 10 leagues south-east from Guayaquil, though by the com-
mon road near 200. The places about Loxa, where this fine sort is found, are
La Sierra de Caxanuma, Malacatos, Yrutasinga, Yangana, Mansanamace, La
Sierra de Boqueron, and a place called Las Monsas.

The bark trees do not grow all together in one spot, but intermixed here and
there with many others, in the woods; it happens indeed sometimes, that
clusters of them are found together, though at present they are much scarcer
than in former times, a great many of the fine large bark trees having been
entirely cut down, that their bark might the more easily be sliced off.

The soil where the best sort thrives, is generally in red clayey or rocky
ground, and very frequently on the banks of small rivers descending from high

That this tree flourishes and bears fruit at the same time all the year round,
is certainly owing to the almost uninterrupted rains, that fall in those high
mountains where it grows, which continue with little or no intermission:
though about 3 or 4 leagues down in the low country, where it is excessively
hot, there are wet and dry seasons, as in other hot countries, the rains begin-
ning in December and ending in May; this season the Spaniards who live there
call temporal, and it is general all thereabouts; whereas what they call paroma
is a cold rainy season, that lasts in all the mountainous places of these coun-
tries from June to November, but especially in the city of Loxa and places
adjoining, where Mr. Arrot has passed 23 or 30 days without once seeing the
sun, and felt the air so extremely cold, that he was obliged always to be wrapped
up in his cloak, and to be in continual motion to keep himself warm. Such
excessive cold so near the line, appears to Europeans incredible; but many
places in these latitudes are so, by their situation and vicinity to high

The properest season for cutting the bark is from September to November,
the only time in the whole year of some intermission from rain in the moun-


tains. Having discovered a spot where the trees most abound, they first build
huts for the workmen, and then a large hut to receive the bark, to preserve it
from the wet : but they let it lie there as short a time as possible, having before-
hand cut a road from the place where the trees grow, through the woods, some-
times 3 or 4 leagues, to the nearest plantation or farm-house in the low country,
whither, if the rain permits, they presently carry the bark to dry. These pre-
parations made, they provide each Indian, these being the cutters, with a large
knife, and a bag that can hold about 50 lb. of green bark ; every two Indians
take one tree, whence they cut or slice down the bark, as far as they can reach
from the ground; they then take sticks about half a yard long each, which
they tie to the tree with tough withs, at proper distances, like the steps of a

Online LibraryRoyal Society (Great Britain)The Philosophical transactions of the Royal society of London, from their commencement in 1665, in the year 1800 (Volume 8) → online text (page 18 of 85)